The present invention relates to a lifting and supporting device for handling and positioning particularly large-surface elements in the shape of panels, especially in plasma processing installations, as well as a corresponding processing method and a device therefor.
During the processing and especially during the coating or etching of semiconductors, silicon wafers for the production of integrated circuits for example, or of dielectrics, as for example glass plates for the production of flat television screens, the substrates, which for the most part are in the form of panel-shaped elements, have to be transported, temporarily supported, etc., or, quite generally, have to be handled in a certain way either during a processing step or between one step and the next. Unlike what happens in other fields of processing logistics, however, this is associated with difficulties, because both the components and the processes are extremely sensitive and even very small perturbations could cause considerable harm to the components or even lead to their complete destruction.
A problem that arises quite generally in the handling of semiconductors, but particularly in the handling of dielectrics that carry such electrical circuits as, for example, thin film transistors, is the problem of the electrostatic charging and the subsequent undesired electrostatic discharge. As can be seen from the schematic illustration of FIG. 6, the various working processes, plasma coating processes being a case in point, but also friction events during the transport of the panel-shaped elements can cause the panel-shaped elements to become electrostatically charged. This charge on the panel-shaped element 4 is schematically represented in FIG. 6 and there indicated by the reference number 8. If the charged panel element is now brought to a different distance from ground potential, as can happen, for example, during the lifting of the panel-shaped element, potential differences will occur on the panel-shaped element 4 and in FIG. 6 are indicated by V1 and V2. These potential differences on the surface of the panel-shaped element can now have the effect of causing an electrostatic discharge across the circuits or thin film transistors applied to the surface. This is schematically illustrated in FIG. 6 inside the frame at the center of the figure. But the electrostatic discharge can lead to the destruction of the component, so that in case of doubt the entire panel-shaped element, complete with its plurality of circuits or thin film transistors, has to be regarded as a reject.
This problem has hitherto been tackled, first of all, by trying to avoid the charging of the panel-shaped elements by, for example, ionizing the surrounding air. But, it has been found that complete avoidance of electrostatic charging is hardly possible in actual practice. Another approach to the solution of the problem is the undesired electrostatic discharge is the one in which all the circuits applied to the semiconductor or the dielectric are short-circuited during the production process by means of the application of additional conductors, so-called bus bars. But this has the disadvantage that it is associated with the greater cost of first applying and subsequently removing the bus bars. Over and above this, the bus bars also constitute obstacles for the remainder of the production process.
Especially in the case of plasma processes, a further problem associated with the handling of panel-shaped elements consists of the fact that the presence of the lifting and supporting devices in the plasma chambers perturbs the plasma, which effects the properties of the elements to be processed with the plasma. In plasma processing installations, the elements that are to be processed with the plasma, e.g., such panel-shaped elements as, for example, silicon wafers or glass plates, are usually deposited on metallic base plates in order to be processed with the plasma. To this end, pins are provided at the edges of the base plate that can be made to descend into the base plate in order to permit the raising and lowering of the panel-shaped elements, so that a gripping device, the arm of a robot for example, with a fork-shaped holder can be inserted under the panel-shaped elements and transport them from one processing station to the next. The pins of the known lifting and supporting devices are arranged at the edge of the base plate, because the pin holes in which the pins are moving constitute inhomogeneities in the metallic base plate and can therefore lead to a modification of the plasma above these regions. However, a modification of the plasma above these regions would have the consequence that in this area, for example, the deposition of coatings or the etching by means of the plasma, would be perturbed. However, since circuits or thin film transistors, i.e. active elements, are not usually applied to the edges of the panel-shaped elements, the arrangement of the pins and the pin holes in these regions does not do any harm. However, as the size of the panel-shaped elements increases and their thickness diminishes, this will once again lead to problems, because pins will now have to be arranged also at the center of the base plate in order to assure adequate support for the panel-shaped elements when they are raised or lowered. In this way, however, the pin holes will create inhomogeneities in the region of the center of the lifting and supporting device, where it would likewise be desirable to have the possibility of producing active areas of the panel-shaped elements. Hitherto, this problem has been solved by producing several finished components on a single panel-shaped element that, on completion of the process, are separated from each other by cutting the panel-shaped element. It is therefore possible to provide appropriate pins in positions corresponding to the cutting regions, because perturbation of the plasma by pins and/or pin holes arranged in these regions will not have any harmful effects. However, since in the case of the production of, for example, flat television screens, we have a situation in which the individual active regions of the panel-shaped elements become greater while the thickness of the panel-shaped elements diminishes, this remedy is subject to certain limitations.
Furthermore it is known, from U.S. Pat. No. 6,228,438 B1 for example, that the elements to be processed in the plasma can be supported on pins in order to form a dielectric layer below the element to be processed. In this case, the pins will once again produce perturbations in the plasma in the neighborhood of the pins. These are attenuated by means of additional recesses around the pins in the base plate.